FIG. 1 illustrates a cellular repeater 100 having a donor antenna 102 adapted to communicate with one or more base stations 104, and a server antenna 106 adapted to communicate with a wireless device 108. Examples of the wireless device 108 include a cellular phone, laptop computer, desktop computer, or personal digital assistant (PDA). Thus, the cellular repeater 100 is suited for an environment such as a home or building, to receive signals from the selected base station 104, boost, or add gain to, the signals, and send the boosted signals to the wireless device 108, and back again from the wireless device 108 to the selected base station 104.
Cellular repeaters 100 usually require radio frequency (RF) isolation between the server and donor antennas, as a signal received by one antenna, to be amplified and transmitted by the other antenna, could return back into the first antenna to potentially cause instability and oscillations. The required RF isolation can be realized either by physical separation (i.e., path loss) between the antennas, or by making the antennas directional, providing a level of signal attenuation in the direction of the other antenna, or by a combination of both physical separation and directional separation techniques.
In a single-box repeater, where the donor and server antennas are both placed in a single enclosure 105, it is not possible to provide the RF isolation by distance (path loss) and therefore antenna directivity has to be used if an appreciable gain is to be realized by the repeater. While it may be possible to use two directional antennas in a single box facing opposite directions to provide some level of RF isolation, such use of directional antennas in a cellular network has adverse effects on network performance. For example, if a directional antenna is not being directed toward the right base station (also called Base Transceiver Station, or BTS) at the time, the antenna could communicate with a base station in which signal strength is suboptimum.
Further, if the antenna is not in the direction of the selected base station, the directionality property of the antenna can reduce the signal level to/from BTS (or MS), attenuating it beyond what is receivable by an omni-directional antenna. This causes excess loss due to the directionality of the antenna, degrading network performance.